Method of manufacturing highly-active carbon



Patented Dec. 14, 1926'.-

UNITED STATES PATENT OFFICE.

EDOUARD URBAIN, 0F PARIS, rnanennssrenon T O URBAIN CORPORATION, A. COR- PORATION OF DELAWARE.

METHOD 0] MILANUFA0'1'UIIRIING' HIGHLY-ACTIVE CARBON.

No Drawing.

substances, the vegetable material will car-- bonize very readily and at a lower'tenaperature than if these substanees'have not been used, and a parently it has been believed that the pro notion of carbon at low temperatures was a factor in its activity. Accordingly, those who have used these materlals have always stopped the calcination at about the time when carbonizatio'n was complete,

that is, at a dull-red heat or a temperature of about 700 C.

I have discovered that far more active carbon can be produced if vegetable material is calcined in the presence of such bodles at a materially higher temperature-which should exceed 800 C. and referably is carried up to a temperatureo about 1000 C. At this higher temperature range, the bodies referred to act in a different way from what they did at a lower temperature, and a new and highly important result is produced. In order to understand this result a certain theoretical discussion should be given.

If one studies absorption by carbons, of gases under conditions of temperature,

pressure and concentration which are far removed from the point of liquefaction of such gases, there is no appreciable difference between the absorpt ve capacity of carbons resulting .from slmplecarboniz'ing of organic matter and the carbons which have been subjected to a. special treatment'by which thev have been made active; in other words, ordinary charcoal and specially-prepared active carbon will, for example, absorb about the same amounts of anhydrous sulphurous acid at the ordinary tem erature when the concentration and there ore the partial pressure are low; However, these two classes of carbons will show very differcnt degrees of absorption when used in connection with va ore of substances which are liquid or so id at atmospheric pressure at or near the temperature at which the absorption is effected. For example,

Application filed March 29, 1928. Serial No. 98,376, I

with benzol of a 'given partial tension, ordinary wood charcoal will absorb only from 5 to 6% by weight of the benzol, while properly activated carbon will absorb 40% or more. classes of carbon have about the same apparent density; their active surfaces, as reflected in the absorption of S0 are on the same order of magnitude, and from this 1t can properly be supposed that they have about the same compactness. Accordingly it is apparent that chemical differences in the two classes'of carbon are more important than their ph sical differences. 1

If one ana yzes the two classes of carbon, it will be found that the differences in the ash are negli ible, but on the other hand, it will be found that the two classes have a very different hydrogen content. The wood charcoal may contain as much as 2% or more'of hydrogen, while carbon activated will contain only .5 of hydrogen, or less.

This is true even where the two This hydrogen undoubtedly forms part of or anic combinations which are distribcarbon cannot be made to retain any such proportion of hydrogen, even after it has been saturated with hydrogen at high pressure. Even if this is done re eatedl it will be found that the active car on wi 1 retain much less hydrogen than the ordinary charcoal. In the same way if the carbon is saturated with' h drocarbons, the latter can, quite readily, e removed by relatively low temperature steaming, without material loss in activity. I

From the foregoing considerations, I have concluded that the absorption of gases by charcoal (including active carbon) is originally an adsorption, that is to say, an action pressure used is readily adapted to go into the. liquid or solvent state. Apparently the presence of hydrogen in the carbon is of primary importance. as influencing this sec ond capillary absorption, for, as-we-have seen, when working with a gas such as S in low concentrations, where; the capillary eifect is negligible, then the adsorption powers of thetwo classes of carbonsdiscussed are substantially identical. From this it follows that the activity of an amorphous carbon of a given density and capacity depends solely upon its purity as reportance, especially during the last twenty years, that high temperatures must not' be used during the activation.

My present invention is based specifically upon the use of high temperature calcination under conditions which will cause the hy-' 'drogen of the carbon masses to .be substantially eliminated. I accomplish this by permeating-the raw material with a substance preferably in theliquid phase, or in solution, which will at high temperatures act rapidly to remove the hydrogen but which will have relatively little effect on the car-- bon masses. For this purpose I may, for

example, use the identical substances which heretofore have been used at relatively low temperatures, such as zinc chloride, or phosphoric-acid. In generahI have .found that many oxides either introduced as such, or formed during the calcination of the substance (such as zinc oxide produced by the decomposition of zinc chloride), will destroy the organic combinations and remove the hydrogen before acting upon the amorphous carbon.

proper temperature shall be attained in order that the oxide shall act in an effective 1 manner, and it is. this necessity that differentiates my said process from all the known processes wherein the same sub stances which afi'ord dehydrogenizing oxides are indeed employed, but in which the de-.

hydrogenizing action is not given its full advantage.

According to my process, an oxide should be selected which will not be reduced by the solid portions of the charcoal at the temfree by the disassociation of hydrocarbons.

perature used, but which will be reduced quite easily by the carbon or hydrogen set The only condition required is that 'the This. means that one should not use an oxide which is too easily reduced such as 1s the case with lead oxide, nor should one use an oxide which is, too diflicult to reduce, as for example, aluminum oxide.

If a suitable oxide is used, the temperature should be high enough to cause a slow breaking down of the hydrocarbons to take place. From this it follows that for all oxides suitable, a favorable 'tem erature is in the neighborhood of 1000 For instance, should I employ zinc chloride, I do not limit the effect to the dehydrating and carbonizing action of this body, which takes place below 700 C. If the action is stoppedat this temperature, one may by washing with dilute hydrochloric acid recover'a good proportion of the zinc chloride employed, and obtaih a carbon which is sufiiciently active for a certain number of uses. But, in such methods, I seek to obtain" a carbon having a great activity, and for this purpose I raise the temperature to 800 or 1000 0., or even more, the temperature being chiefly limited by the necessity of using retort furnaces whereby the product-will be protected from oxidation by air or fumes. l

' The dehydrating action of the zinc chloride, which takes place at relatively low temperature, is accompaniedby a marked hydrolysis, and hydrochloric acid is disengaged in abundance, whilst the major part of the zincremains inthe carbon in the state of oxide. As I above remarked, when this action is completed, i. e., near 700 0., the result is acarbon which will, even at thls point, possess a marked activity when it is freed from the zinc oxide by washing with dilute hydrochloric acid. But Ido .not stop the operation at this stage, and I raise the temperature until the zinc oxide is reduced by the hydrogenized bodies thereby effecting a removal. of hydrogen from the carbon. Vapors of zinc and zinc oxide will be disengaged, corresponding'to the decomposition of the last remaining hydrogenized compounds.

the unfavorable action of high temperatures such as I employ, the resulting carbon is v extremely active.

My said process is of an absolutely general nature. By way of example. I have found that an excellent carbon can be obtained b adding oxychloride of arsenic to any sui ablevegetable substance, and from a certain temperature onward, this will leave in the A carbon a residue of arsenious acid; the temtion at a sufiicient temperature, shall be accompanied by the oxidation of the hydrogen 1n combination in the hydrogenized substances which withstand the calcination. Phosphoric acid may be given as an example of ternary compounds, and I may even employ more complex bodies such as the monocalcic or bicalcic phosphates.

In view of the preceding, I need not lay stress upon the fact that the useful efiect does not consist in the dehydrating or carbonizing action of such bodies at low temperatures.

Sulphuric acid and ferric 'chloride are powerful dehydrating agents, but the carbons obtained by the use of these agents still contain a considerable amount of combined hydrogen, and have but a moderate absorbing power, being inferior to the carbons obtained by oxidation in superheated steam, which latter is however neither of a dehydrating nor'a carbonizing nature, or is only so by reason of its high temperature,

But the complete dehydrogenation can not be had by means of steam, since after a certain temperature, which must however be exceeded to obtain the complete dehydrogenation,-the steam will act with like facility upon amorphous carbon which is thus destroyed in the same proportions as the hydrogenated bodies.

As stated above, I set aside the oxidizing substances, which could only be utilized in the form of vapors which are supplied during the calcination; such substances act chiefly on the outer parts of the carbonized masses, and in these parts they oxidize the amorphous carbon, whilst'they have but little action on the hydrogenized substances contained in the better protected parts of-the carbon. Moreover, I prefer not touse the substances which can be mixed with the carbonizable material only as solids, as they will not permeate and give the results that can be obtained by the use of liquids or solutions.

Should it be found that with oxidizing agents. whose volatility is not absolutely ne ligible at the high temperatures attained, this volatility prevents the continuation of the chemical action for a sufficient length of time to obtain a very active carbon, it will be necessar to stop the calcination'of this carbon, an to again impregnate it with the oxidizing agent, and to effect a new calcinetion, and this operation may be repeated as often as required.

In like manner, I may efiect successive 'calcinations wherein various oxidizing agents are em loyed in succession, and this may be carrier out for different reasons, for

example to afford the solubility of the inorganic matter contained in the carbon, or on the contrary to render this matter quite insoluble. i

In some circumstances, particularly where the oxidizing agent likewise has'a dehydratmg actionlat lower temperatures, it may be advantageous to use a relatively large amount of such agentto attain the maximum dehydrating action, but it may be disadvantageous or undesirable to allow the full amount of such material to remain in the carbon during the final calcination. When such a circumstance arises, I use the amount of material desired to obtain the carbonizing or dehydrating effect, and heat the mass until it has become carbonized and sufiiciently strong to withstand washing, but not up to the temperature-where such material decomposes and starts to remove hydrogen.- The excess of the oxidizing agent can then be washed out, care being taken to leave enough of this agent in the material to give the desired dehydrogenating action. The washing can of course be carried out by any necessary solvent which will not have an injurious effect on the carbon; and may be repeated several times so as to obtain solutions which are as rich as possible; for example, one may first wash the material with a solution obtained from the second washing of a prior operation, and then give the material a second washing with the solution used for the third washing from a prior operation, etc.

- and finally one can wash the material with the solvent alone. The solution which has been used three times can be re-concentrated or can be enriched by added quantities of the reagent and then re-used. In some instances where the reagent is of no particular value, it may still be desirable to wash out the excess, so as to eliminate, as far as possible, the oxidation of the carbon itself by such oxidizing agent.

If the oxidizing agent is valuable, care should be taken to recover as much as possible either by a preliminary washing such as has been referred to, or by the method in which the final calcination is carried on.

For example, if zinc chloride is used, whichlater is converted into zinc oxide, therewill be evolved during the final calcination,

any desired purpose.

, I oxideior metallic zinc that may remain in the mass.

If phosphoric acid or monocalcium phosphate is the oxidizing agent selected, it Wlll. be found that fumes of PH will be evolved as the temperature approaches 800 C. The temperature should be raised above this oint, and as it goes up, there Wlll be chiefy an evolution of P H and finally of phosphorus. The maximum benefit is attained by raising the temperature to the point where phosphorus is largely evolved, and in this case, particularly if the phosphate was used as the oxidizing agent, one obtains not only the valuable active carbon,

' but also the phosphorus as a by-product. Ac-

tivation is practically completed. when the evolution of phosphides ceases, but for some purposes the carbon should be free of phosphorus and the method of distilling 01f the phosphorus is an economical method of removing it. The phosphorus may be separated from the other fumes in any desired Way, and a very advantageous manner is to let the gases pass over active carbon which will retain the phosphorated hydrogen and phosphoric vapors which have escaped condensation. The residual gases will be found to lee-combustible and may be burned for The phosphorus can, if desired, be burned with the minimum amount of air necessary to obtain phosphoric anhydride. It is advantageous to separate the phosphorus from the other gases, as otherwise a larger amount of air will be necessary to carry on the combustion, and there will be difiiculty in separating the-finely divided phosphoric anhydride, which} is hydride, from the gases that will rexna However, if desired, the evolved ases m be burned immediately and the p osplio anhydride (P 0 formed may be collected in a suitable condensation and apparatus. j v It is even possible to control the 01) tion so that a large amount of phosphorus can be obtained; for example, one may use as much as four parts of monoealcium phosphate to one part of carbqnizable material such, for example, as peat or animal mat-.

ter. Carbon made by other processes may 1 be activated to a certain extent in this way,

but in such case, the suggested proportion is to use two parts of monocalcium phosphate to one art of charcoal: Under these conditions ca cination and conversion willbe complete in from eight to twelve hours. The proportions which are given above are only intended asindications. It may be said generally that in order to obtain very active carbons, a smaller quantity of reducing agent should be used, and in any evcnt,rthere'should be a large excess of carall of the hydrogen is eliminated.

In order better to understand my invenby "tion fi mass was then put in a closed retort and the; temperature raised. As' the temperaera-i 'turepassed beyond 700 (land approached bon which will not be oxidized b the reduction of the acid constituents of t e monocalcium phosphate,

In' carrying out my invention, I prefer to use a vegetable material such as peat which is finely ground and mixed with the oxidizing'material and sufiicient liquid to give the finished product the desired capacity, as is explained in my co-pending application, Ser. No. 25,707, filed April 24, 1925. The mixture is then molded as explained in that application, dried, and calcined at the temperature necessary for producing the dehydrogenizing effect which has been referred to. The resulting carbon may then begwashed, as has already been explained, and if necessary may be once more calcined; Of course other forms of vegetable material may be; used and therefore in the claims I use the term cellulosic material a's""defining the type of material of vegetable origin available in my process.

By carrying outthe process of manufacturing active-carbon asoutlined in this apan operahle=density t' ionljexample, having a compactness'betweeii'"i7 and .15) which will have a hydrogen content substantially --bel ow By the selection of favorable is taken in conducting the operations, it can be so completely removed that, forpractical purposes, it maybe said that substantially tion, one example is given:

Finely ground peat moss was mixed with form a st-iif paste. This was extruded, gran- }ulated and dried for one hour at a temperature sufiiciently high to cause some carbonization of the peat to take place. The

800 (3., there was an evolution of PH As the temperature was kept rising, P H was evolved, and finally there was an evolution of phosphorus. The temperature was maintained at approximately 1000 C.- until no more phosphorus Wasevolved. The phosphorus fumes were absorbed in previously activated carbon and later converted into phosphoric anhydride by burning with a minimum quantity of air. The carbon was allowed to cool slowly, washed with dilute hydrochloric acid, dried, andagain calcined for about three hours at a temperature of about 800 C. The resulting product was found to have a density of about 0.3, and on analysis was found to have a hydrogen content of only 1%. It showed very high plication,oneranreadily obtain carbons of I a, solution of .mono'calcium phosphate to i v 7 activity for the absorption of variousabsorbed 65% by .lution of phosphides.

defined in claim 1, in.

' 2. A process as which the material is heated during calcinationuntil there "is an evolution of phos phorus vapor. i

3. A process of manufacturing. activecarbon and recovering a reagent in a form adapted for use manufacturing additional quantities of activecarbon which comprises the steps of subjecting cellulosic material to the action of a substance of acid reaction comprising oxygen and phosphorus in chemical combination at atemperature sufliciently high to cause an evolution of phosphorus and continuing such heating until the evolution .of phosphorus substantlally'ceases.

' prising a material ada ,4. The process of producing active carbon and phosphorus which comprises the steps of treating monocalcium phosphate and a substantial excess of cellulosic material in a retort at a temperaturehigh enough to cause phosphorus to be largely evolved.-

5'. The -proces s.of producing active carbon which comprises the steps of permeat ing cellulosic material with aliquid com perature below 700 as a dehydrating agent and at higher temperatures to efiect the removal of hydrogen by chemical reaction, and calcining such material in a substantially closed retort permitting the escape of gases, at-a temperature substanmaterial. or the hon, which comprises t ted to act at a temtially above 700 0. and sufliciently high to cause said latter reaction to take place.

6. A process as defined .in claim 5, in which a part of the reaction products of said dehydrating material is washed out after carbonization has taken place and before the final calcining temperature is reached.

7 The process of producing active carbon which comprises .the steps of mixing together cellulosic material and a dehydrating oxidizing agent which can be heated 1n .the presence of. such cellulosic material to 700 0. without being fully volatilized, and heat- 8. A --process as defined in claim 7, in which the mixture is heated to a temperature of approximately 1000 C.

and

im; such mixture to a temperature above X 9. In the process. of producin active carbon, the step of permeating ce lulosic material or the like with a solution of a substance adapted.to be brought in the presence of such cellulosic material to relatively high temperaturesat which that-'su stance is-adapted, in the presence of the cellulosic material to decompose and generate products adapted to combine with hydrogen; and

pose, to remove the hydrogen.

10. carbon, the steps of permeating ccllulosic like with phosphoric acid and then :-heating the material to the P0130 where the phosphoric .acidisf decomposed 1 with the formation of phosphides an "hy-- g5 drogen is largely removed. p roduclng actlve. cal.-

11. The process of gether cellulosic material and a substance comprising the P0 radical acid .comb1- nation in excess of bases present, and heatthereafter heatingv to thetemperature at which such'substancewill decom In the process "of producing active e steps ofmixing tov I I ing such mixture until elemental phosphorus is evolved.

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